Selenium rectifier with varnish intermediate layers



Nov. 24, 1953 H. E. LAUCKNER 2,660,697

SELENIUM RECTIFIER WITH VARNISH INTERMEDIATE LAYERS Filed Sept. 18, 1951 FIG. 3.

FIG. 4.

A ORNEY Patented Nov. 24, 1953 SELENIUM RECTIFIER WITH VARNISH INTERMEDIATE LAYERS Hans Eugen Lauckner, Weissenburg, Bayern, Germany, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application September 18, 1951, Serial No. 247,161

'Claims priority, application Germany September 21, 1950 6 Claims.

It is known practice to increase the blocking voltage of selenium dry plate rectifiers by applying a thin intermediate layer of insulating inaterial such as varnish to the semi-conducting layer. It is relatively diiiicult, of course, to prcduce this intermediary layer in equal quality. Accordingly, the electric values of such rectiflers varies. ln particular there are differences in the forming qualities which take effect in the rin ished rectifier discs since in the case of a great number of discs it is not possible to form each disc by itself.

It has been proved that according to the invention rectiers with extremely uniform qualities are obtained, especially rectiliers with a reproduceable blocking characteristic, if the Varnish is applied as a screen or raster instead or an evenly distributed varnish intermediate layer. After application of the varnish the back electrode is then applied. It will be of advantage to apply a screen composed of lines or dots to the selenium surface by a printing process.

Tests showed that the cover should not exceed a certain part of the selenium layer. E. g. a too great cover is applied in case of a line shaped screen wherein stripes of the free selenium sur:- iace of 0.15 mm. width alternate with varnish stripes of 0.25 mm. width; in this case the effect of an evenly distributed varnish layer results again. The covering of the selenium surface, i

therefore, must not reach these proportions. lt has to be noted, however, that the proportions are dependent on the geometric structure of the layer system, and also on the fmeness of the varnish screen.

The resistance of the rectifier in the forward direction is reduced by the arrangement of the present invention without impairing the blocking voltage. To explain such behavior it can presumably be pointed out that the arrangement may concern an approximation to the conditions of the point detector and that different current lines may be more decisive for the blocking phase of the rectifier than for the passing phase.

The behaviour of the system may be understood from the conditions of point-shaped contacts (see Electric Contacts, a book by Ragnar Holm) and shall be explained with respect to the accompanying drawings in which Fig. 1 shows a scheme of the current distribution in a system in which a homogeneous body is contacted by another body of a sharp iorm along a small area (point contact). In Fig. 2 the homogeneous body is subdivided into two regions of diierent resistivity. rIhe schemes corresponding to Figs.

3-5 shot.7 interrupted coats of lacquer, varnish, or 'the like, applied to the semiconducting layer before depositing the counterelectrode. Fig. 1 is a sectional view ci a complete cell including base element, semi-conductor, insulating screen layer, and counterelectrode.

Sup-posing in Fig. l a circular contact area of point i, which is small in comparison with the thickness of the homogeneous body 2, the current distribution indicated by the lines 4. It is cbvious that the swelling out of the lines will be decreased when substituting a given body of a certain resistivity by another one of the same shape or size but having a comparatively higher resistivity. This case has been realised in Fig. 2 in such a manner that a point-shaped contact touches a layer of a high resistivity contacting a body or low resistivity in the entire extension of the touching surface of these two bodies. In this case the current distribution is indicated by lines d'.

Whilst the scheme of Fig. 1 corresponds to point contact rectiiiers in which the current is flowing in the open or forward direction, the scheme of Fig. 2 is an image of the current ow in the inverse direction, where a blocking layer 3 has to be provided. Within the range of high resistivity the lines may be supposed to run almost parallelly and to swell out when entering the material of better conductivity.

When regarding the relation between the direct resistance and the blocking resistance as a function oi" the diameter or the shape of the contact area, the resistance in the blocked direction will increase to a higher percentage than in the opposite direction when decreasing the contact area. Thus the advantage of the invention may be seen in the process to replace a contact area, given by occasional perforations in a normal blocking layer (artificial or not), by a greater number oi smaller contact areas of an arbitrary defined shape. It should be understood that this; explanation of the advantageous effect of the invention should not exclude another theory o' the function of the device according to the invention.

Examples oi the distribution of the insulating material have been drawn in the further iigures. Corresponding to Fig. 3 tine parallel lines 5 of insulating material have been provided. In Fig. 4 two systems of rectangular crossed lines 5 and 6 have been shown.

Another embodiment oi the invention is represented in Fig. 5, where iine points 'l in regular distribution may be produced by a printing process. All gures have not been drawn in true scale. In at least one directionlines in the Width, points in the diameter-thesize of the intermediate lacquer coating should be Aof the order of thickness of the semi--con'du'ctig layer and less.

A complete cell is shown in Fig. 1 having a base element 8, a semi-conductor 9, insulating screen layer I and counter-electrode Il. The insulat-v ing screen layer i0 shown in Fig. 6 is of the form shown in Fig. 3.

The thickness of semi-conducting layers 'usdally lies between 0.03 and 0.10 nim. Thus the width of the lacquer stripes in Figure 3 or the diameter of the lacquer dots ih Figure 5 should approximately have these values. On the other hand, the area covered with lacquer shall a'r'niiht to {Z0-70%, preferably 40-60% of the total area. Hereby the higher percentages are to be applied in case of ne rasters only, i. e. for instance in oase of narrow lacquer/stripes. In the above example of a raster with lacquer stripes of 0.25 nim. Width alternating with uncovered stripes of 0.15 mm. width, 'howeverAi the lacquer stripes are covering only 62.5% of the total area, butldu'eA to their great Width they are taking equal effect as an uninterrupted lacquer layer and therefore are not suitable for the reduction to practice of thev invention. n l

While I have described above the principles of my invention in connection with speciiic methods, it is to be clearlyA understood that this description is made only by Wav of example and not as a limitation to the scope of my invention.A

What is claimed is:

1. Selenium rectier, in which an intermediate layer of insulating material is placed between the semi-conducting" layer and thbck electrode for an improvement in ure tracking voltage, characterized in that this intermediate layer takes the form of a screen (raster). 2.*S'e1enium rectifier as claimed in claim 1, and in which the insulating screen is made from some varnish.

3; )Seleiun reti'er as claimed in claim 1, and in t'vhic the scr'fi is composed of lines.

Slgiiuiir'etifier as claimed in claim 3 in ivhih the Width the lines going in one directin are f the order of the thickness of the semiconducting layer or less.

`5. AS'elriii ctier as claimed in claim 1 in which the screen is composed of dots.

6. Selenium rectifier as claimed in claim 5 in which the dots have a diameter of the same order as the thickness of the semi-conducting layer or less;

HANS EUGEN LAUCKNER.

References itd in the file of this patent UNITED STATES PATENTS 

1. SELENIUM RECTIFIER, IN WHICH AN INTERMEDIATE LAYER OF INSULATING MATERIAL IS PLACED BETWEEN THE SEMI-CONDUCTING LAYER AND THE BLACK ELECTRODE FOR 